Novel polymerization catalyst based on hydrogen peroxide and thioglycolic acid



United States Patent NOVEL POLYMERIZATION CATALYST BASED ON TAJYIDROGEN PEROXIDE AND THIOGLYCOLIC James M. Hawkins and Donald J. Shields, Kingsport,

Tenn., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 328,118, Dec. 4, 1963. This application Nov. 16, 1966, Ser. No. 594,659

7 Claims. (Cl. 260-80) ABSTRACT OF THE DISCLOSURE A catalyst combination of hydrogen peroxide and at least one compound represented by the formula ll HS-R-C-OH wherein R is an alkyl radical containing from 1 to 18 carbon atoms, has been found to form good yields of polymer having an inherent viscosity above 0.5 at temperatures less than 50 C. The preferred catalyst combination is hydrogen peroxide and at least one member selected from the group consisting of thioglycolic acid, amercaptoproprionic acid and fl-mercaptoproprionic acid.

This application is a continuation of application Ser. No. 328,118 filed Dec. 4, 1963, now abandoned.

This invention relates to homo and copolymerizations of chemically unsaturated materials and particularly concerns novel catalyst systems for such polymerizations.

In the field of polymer chemistry, it is especially desirable for most polymer applications to employ a catalyst which will give a good yield of high inherent viscosity (above 0.5) polymer at a commercially practicable rate. The high I.V. is necessary for such properties as toughness which is required for films, fibers, and molded articles in general. Moreover, for many applications the color of the polymer should be stable.

Objects of the invention therefore are: to provide a process for forming high-I.V., tough, color-stable polymers at high rates and in good yields; and to provide improved catalysts for aiding in this process.

These and other objects have been achieved in accordance with the present invention through the discovery that hydrogen peroxide, when activated with at least one compound represented by the formula wherein R is a member selected from the group of divalent hydrocarbon radicals containing from l-18 carbon atoms, at low temperatures, rapidly promotes high-I.V. polymer formation in good yield without adversely affecting polymer color stability. In a more specific sense, the novel catalyst systems comprise hydrogen peroxide and a mercaptocarboxylic acid selected from the group consisting of thioglycolic acid (mercaptoacetic acid), a-mercaptopropionic acid and fi-mercaptopropionic acid, with the thioglycolic acid being the most elfective and therefore preferred.

The unexpectedness of such results is evidenced by the fact that activators. and in particular mercaptans, are known to prevent high-moleeular-weight and high-I.V. polymer formation by virtue of their chain transfer activity; see Vinyl and Related Polymers, Schildknecht, p. 99.

The hydrogen peroxide component of the catalyst system is of course a well-known free radical generator. Its commercial use however is limited by its low catalyzing activity at temperatures less than 50 C. This low activity was demonstrated by charging 75 parts of styrene, 25 parts of acrylonitrile, 0.1 part of phosphoric acid, 5 parts of Igepal CO-850 [nonylphenoxypoly(ethylenoxy)ethanol], 300 parts of deoxygenated water and 1.0 part of hydrogen peroxide to a reaction vessel maintained at 25 C. The contents were observed over a 24-hour period and no reaction was evident.

At temperatures above C., e.g., hydrogen peroxide does become a more active polymerization catalyst, but at such temperatures the polymers formed had extremely high inherent viscosities and an objectional color formation. For example, a /25 styrene/acrylonitrile poly- Igij; made using 1.0% of H 0 at 50 C. had an I.V. of

As taught by the prior art, the catalytic activity of hydrogen peroxide at lower temperatures may be markedly 1mproved by activating the same with inorganic salts such as ferrous ammonium sulfate, but the residues of these activators in the polymer induce color instability. For example, iron residues from the ferrous ammonium sulfate lead to polymers that discolor severely under normal molding conditions.

According to the present invention, hydrogen peroxide is activated with the aforesaid mercaptocarboxylic acids which leave only innocuous residues in the polymer. It is noted that these mercapto acids are color stabilizers in their own right and residues thereof actually enhance color stability. It is also notable that an additional advantage of these acids is their solubility in water which allows them to be readily washed from the polymer, if desired. Moreover, these acids are particularly effective in aqueous systems and at temperatures of less than 50 C. produce polymer in excellent yield having an I.V. of less than .8. The weight ratio of these activators to hydrogen peroxide may be varied between about 005/] to about l/l, with 0.2/1 to 0.4/1 being preferred for most polymerizations. The preferred concentration of catalyst is between about 0.5 to about 2.0% by weight of the total monomer although other concentrations may be employed, depending upon the desired speed, etc. of the reaction. The present catalyst systems are effective in the pH range from about 1.5 to about 8 with a pH between 3 and 5 being preferred. These systems are also effective for homogenous and heterogenous aqueous polymerizations.

Where the polymerizations of water-insoluble monomers such as styrene, vinyl acetate, acrylic and methacrylic esters, are carried out, any of a wide variety of surfactants or dispersing agents may be employed without affecting the operation of these catalyst systems. Surfactants useful for dispersing such monomers include Duponol ME (sodium lauryl sulfate), Aerosol OT (dioctyl ester of sodium sulfosuccinic acid), Igepal (IO-850 [nonylphenoxypoly(ethyleneoxy)ethanol], and Ultrawet 30 DS (alkyl benzene sodium sulfonate). Other mercaptans, such as normal or tertiary dodecyl mercaptans, are useful as chain transfer agents and may be admixed with the present activators if desired.

As aforesaid, the present catalyst system are efiective for the bulk, solution or suspension homoor copolymerizations, whichever method is most desirable for the particular monomer or monomers, of a large variety of monomers including acrylic and methacrylic acids and their esters, amide and nitrile derivatives, styrene and its derivatives, vinyl esters, dienes, and olefins such as ethylene and propylene. A comprehensive list of applicable monomers is found in US. Patent No. 2,396,785.

The following examples will serve to further illustrate the invention. In these examples the rate of reaction is roughly inversely proportional to the induction period.

'Polymerizations having induction periods of longer than about 10 minutes have been found commercially impractical. The toughness of the polymer product is roughly proportional to its I.V., products having I.V.s below about 0.50 being too brittle for many applications. Polymers having I.V. of greater than 2 cannot be molded by conventional methods as the polymer degrades before melting.

Example No. 1

This example shows that hydogen peroxide when activated with thioglycolic acid does polymerize styrene and acrylonitrile in high yields at 25 C. to give useful, high I.V. product.

Seventy-five parts of styrene, 25 parts of acrylonitrilc, 0.1 part of phosphoric acid, parts of Igepal CO850, 300 parts of deoxygenated water, 1 part of hydrogen peroxide and 0.3 part of thioglycolic acid were charged to a stirred reaction vessel and maintained at 25 C. Polymerization, as evidenced by the formation of insoluble polymer, began after an induction period of 6 minutes. The product, which was obtained in 97% yield after 6 hours, had an I.V. of 0.87. The color stability was determined by heating a sample of the polymer minutes at 200 C., and comparing its color with standard color controls. Color controls were rated 1-16, 1 being pure white and 16 being the brown color developed when a persulfate/bisultite catalyst is used. The polymer prepared above had a color rating of 3. This was whiter than most commercial plastics and permitted the preparation of clear, true colors from standard pigments incorporated in molded specimens of the polymer.

Example No. 2

This example shows that the hydrogen pCTOXldC-lltlttglycolic acid systm is also an effective polymerization catalyst at 70 C.

Seventy-five parts of styrene, 25 parts of acrylonitrile, 0.1 part of phosphoric acid, 5 parts of Igepal CO-850, 300 parts of deoxygenated water, 1 part of hydrogen peroxide and 0.3 part of thioglycolic acid were charged to a reaction vessel and the temperature thereof raised to 70 C. The polymerization was observed after an induction period of 6 minutes. After 4 hours, a 98% yield of product having an I.V. of 0.75 and a color rating of 3 was obtained.

Example No. 3

This example shows that other mercaptans may be used with the thioglycolic acid.

Seventy-five parts of styrene, 25 parts of acrylonitrile, 0.1 part of phosphoric acid, 5 parts of lgepal COS50, 300 parts of deoxygenated water, 1 part of hydrogen peroxide, 0.3 part of thioglycolic acid, and 0.1 part of TDM were charged to a reaction vessel maintained at 25 C. Polymerization was observed after an induction period of 5 minutes. After 6 hours, a 95% yield of a polymer having an I.V. of 0.52 was obtained. The polymer was white in color. (TDM is tert-dodecyl mercaptan.)

The following examples illustrate the utility of other mcrcaptocarboxylic acids as activators for H 0 Example No. 4

This example shows that hydrogen peroxide when activated with [i-mercaptopropionic acid, does polymerize styrene and acrylonitrile in good yields at 25 C. to give a useful, medium-high I.V. product.

This run was carried out in the identical manner to Example I except that 0.3 part of B-mercaptopropionic acid was used instead of thioglycolic acid. Polymerization began after an induction period of 8 minutes. The product, obtained in 90% yield in hours, had an I.V. of 0.7 and a color stability rating of 4.

Example No. 5

This example shows that hydrogen peroxide when activated with wmercaptopropionic acid polymerizes styrene and acrylonitrile in good yields at 25 C. to give a useful, mediumhigh I.V. product.

This run was carried out in the identical manner to for 5 lit) Example 1 except that 0.3 part of a-mercaptopropionie acid was used instead of thioglycolic acid. Polymerization began after an induction period of 8 minutes. The product, obtained in 92% yield in 8 hours, had an I.V. of 0.75 and a color stability rating of 5.

The following example illustrates the relatively inferior color stability resulting from the use of other peroxidic catalysts.

Example No. 6

Sixty/eight parts of styrene, 32 parts of acrylonitrile, 900 parts of H 0, 1.0 part of ammonium persulfate, 0.75 part of sodium metabisulfite, 1.0 part of TDM, 3.75 parts of Alipal CO436 [ammonium salt of a sulfate ester of an alkylphenoxypoly (ethyleneoxy) ethanol], and 1.25 parts of Igepal CO-SSO, were placed in a standard polymerization vessel for hours at 50 C. The polymer had an I.V. of 0.6 and a poor color stability rating (brown) of 15.

The following examples illustrate the utility of the present catalyst systems for polymerizing a variety of monomers without adversely affecting the color stability of the products.

Example No. 7

The same procedure as in Example 1 was followed, except that mcthacrylonitrile was used in place of styrene. The polymer yield was 90%, I.V. was 0.8, and the color stability rating was 5.

Example No. S

The same procedure as in Example 1 was followed, except that wmethylstyrene was used in place of styrene. The polymer yield was 91%, I.V. was 0.75, and the color stability rating was 5.

Example No. 9

The same procedure as in Example 1 was followed, except methyl methacrylate was used in place of acrylonitrile. The polymer yield was 94%, I.V. was 0.85, and the color stability rating was 5.

The following example illustrates the use of the present catalyst in a bulk polymerization.

Example No. 10

.- H 0 and thioglycolic acid were added to a 70/30 styrene/methyl methacrylate mixture. After heating at C. for 15 hours, a 92% yield of polymer having an I.V. of 1.0 and a color stability rating of 4 was obtained.

The following example illustrates the use of the present catalyst in a solution polymerization.

Example No. 11

The following table shows the results obtained by repeating Example 1 at temperatures of 10, 20, 30, and C.

Example NO. 13

The following table shows the results obtained by repeating Example 1 at temperatures of 10, 20, 30, 40 and 50 C. without thiogly-colic acid.

TABLE 11 Temperature, Percent LV.

C. Conversion c l 30 i 40 i 50 8?. 3

I No polymer. Slight indication of some polymer.

Example No. 14

The following table shows the results obtaincd by repeating Example 1 at temperatures of i0, 20, 30, 40 and 50 C. using 0.3 part of teri-dodecyl mercaptan in place of thioglycolic acid.

TABLE III 'Iltllliitltlttll't, Percent LV. (3. Conversion l0 r r 2U s 30 40 78 50 03 (l l Slight indication of some polymer.

acrylamide, methacrylamide, acrylonitriic, methacrylonitl'iie, styrene and vinyl esters at a temperature less than C. and a pH range from about 1.5 to about 8 with a catalyst comprising hydrogen peroxide and at least one mercapto carboxylic acid represented by the formula HsRi i wherein R is an alkyl radical containing from 1-18 carbon atoms, the weight ratio of said rnercaptocarboxylic acid to hydrogen peroxide being between about 0.05/1 to about 1/1.

2 A process according to claim I wherein said catalyst is hydrogen peroxide and thioglycolic acid.

3. A process according to claim 2 wherein said cata- 'st is used in an amount of from about 0.5 to about 0%, by Weight, based on the amount of polymerizable ethylenically unsaturated polymerizablc material.

4. A process according to claim 3 wherein said cata lyst comprises hydrogen peroxide and thioglycolic acid in a Weight ratio of from about 0.2/1 to about 0.4/i.

5. The process of claim 1 wherein the niercaptocarboxylic acid is selected from the group consisting of thioglycolic acid, a-mercaptopropionic acid and fi-mercaptopropionic acid.

6. The process of claim 5 wherein the mercaptocarboxylic acid is u-mercaptopropionic acid.

7. The process of claim 5 wherein the mercaptocarboxylic acid is B-mercaptopropionic acid.

References Cited UNITED STATES PATENTS 2,635,090 4/1953 Basdekis 260-85.5

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION "No. 3 388, I09 June II 1 1968 James M. Hawkins et 211.

It is certified that error appears in the above identified patent and that said Letters Patent are herebycorrected as sbovn below:

Column 1, line 67, "Vinyl and Related Polymers" "should be italicized. Column 3 line 3, after "having" 'insert' an line B after "give" insert a e--. Column 6, lines 6 to 8. the formula should appear as shown below:

Signed and sealed this 10th day of March 1970.

(s EAL) Ancat;

Edward M. Flasher. TL WILLIAM E SCHUYLER TR Atlcsu'ng Officer Commissioner 0? piltefljtg 

